This work attempts to bridge the gap between descriptive and theoretically inclined accounts by focussing on four issues concerning Spanish -dor derivation, namely restrictions on the base, noun-based -dor derivations, the nature of the -dor, -tor, -sor, -or, and -dora forms, and the grammatical category of -dor derivations. It is shown that the Spanish -dor suffix associates with verbs having an external argument (i.e. with transitive and unergative verbs) and that the derivation refers to the base verb's external argument. In addition, it is argued that noun-based -dor derivations are based on the event's complement noun. Moreover, it is argued that there is only one nomina agentis forming morpheme having the form -dor, and that some verbs have both a patrimonial and an erudite allomorph. Finally, -dor derivations are found to be basically adjectival, the nominal variant resulting from the addition of post-derivational idiosyncratic pieces of lexical information.